ES2847198T3 - Building elements made of binders that harden by combined hydration and carbonation - Google Patents

Abstract

Method for manufacturing building elements comprising the steps: - providing a binder comprising at least 8% by weight of ternesite, at least 15% by weight of dicalcium silicate and at least 5% by weight of ye'elimite, each relative to the total binder, as hydraulically reactive phases - mix the binder with water to form a paste - melt the paste into the desired shape for the building element - hydraulically react the paste to form hydrated phases and create pores additional capillaries and - harden by carbonation to provide the building block.

Description

DESCRIPTION

Building elements made of binders that harden by combined hydration and carbonation

The present invention relates to new building elements obtained from binders that depend on hydration with subsequent carbonation to harden.

Cement and products made with it such as concrete, mortar, etc., are very widespread and versatile construction materials. However, cement is also responsible for a considerable amount of energy consumption and CO ² emission, as well as requiring large amounts of valuable raw materials. Thus, many different proposals have been made to save natural raw materials, energy and CO ² emission.

One of them is the use of binders that harden by means of carbonation, see, for example, US 2011/0165400 A1, US 2012/0312194 A1 and WO 2016/022485 A1. By itself, reducing the Ca / Si ratio in the raw material reduces the amount of CO ² released and its absorption during hardening multiplies the effect. This proposal and others are also described at https://www.technologyreview.com/s/ 535646 / what-happened-togreen-concrete. Accordingly, Novacem is based on the replacement of Portland cement with magnesium oxide material that hardens by carbonation. Calera reacts carbon dioxide from exhaust gases to form calcium carbonate powder (vaterite polymorph) which, in turn, is useful as a binder (forming continuous aragonite structures). Carbstone and Solidia are based on materials that harden directly by carbonation.

However, unlike the hardening of Portland cement by hydration with the water present in the paste, carbonation binders require CO ² in relevant quantities and also in high concentration when hardening takes place without long curing times. Even if there is CO ² in the pulp pore solution, its amount is normally too low. Supplying the surrounding atmosphere by diffusion takes too long. Thus, elevated temperatures and aqueous solutions of CO ² or CO ² at high pressure are considered necessary. These are expensive and also not possible for all uses.

Surprisingly, it has now been found that binders comprising ternesite, dicalcium silicate and ye'-delimit as hydraulically reactive phases hydraulically set and harden to provide carbonatable phases with porosity allowing improved carbonation hardening. The hydraulic reaction provides setting, optionally some hardening and green strength of the binder paste and at the same time creates carbonatable phases and, by self-drying action, porosity for improved and rapid carbonation hardening. Of course, it cannot be excluded that some carbonation already occurs during the hydration step due to the carbon dioxide available in the paste and that some hydration continues to occur during the carbonation step as long as hydratable phases and water are present. But the main reactions are hydration in the first step and carbonation in the second step.

Therefore, the above objects are solved by building elements made from a binder comprising at least 8% by weight of ternesite, at least 15% by weight of dicalcium silicate and at least 5% by weight of ye'elimita as hydraulically reactive phases, which is reacted hydraulically to form hydrated phases and capillary pores that allow hardening by carbonation by providing the building element. The sum of all the components, including other phases including the non-reactive phases, amounts to 100% by weight.

To simplify the description, the following abbreviations that are common in the cement field are used herein: H - H ² O, C - CaO, A - ALO ³ , F - Fe2O3, M - MgO, S - SiO ² and $ - SO ³ . The compounds are named mainly by the pure form, without explicit mention of solid solutions, substitution of foreign ions and impurities, etc., as is usual in technical and industrial materials. As is known to the person skilled in the art, the exact composition of the phases described may vary due to replacement with foreign ions. Such compounds are encompassed when the pure form is mentioned herein, unless expressly stated otherwise.

Dicalcium silicate is used herein as the term for various types of dicalcium silicate forms such as, but not limited to, belite, gamma-C ² S, and different types of alpha-C ² S. Typically, there are dicalcium silicates in various polymorphs in clinkers. as ordinary Portland cement (OPC) and calcium sulfoaluminate (CSA) and form complex solid solutions incorporating foreign elements. These solid solutions are also included in the term dicalcium silicate. Ye'elimita designates the C4A3 $ phase which includes especially forms where Al is substituted by iron also in substantial amounts of up to 80% substitution. Ternesita means C5S2 $.

The term "reactive" means hydraulic reactivity unless otherwise specified. Hydraulic reactivity refers to the reaction of a compound with water or other water-containing compounds to form hydrated phases including a reaction of two or more compounds taking place simultaneously.

In the present specification, clinker designates a sintered product obtained by calcining a raw material at a high temperature and containing at least one hydraulic phase. Calcinar means a change of one or more starting material properties such as chemistry, crystallinity, phase composition, spatial arrangement and bonding of the atoms in the lattice produced by the supply of thermal energy. The starting material can be a single material, but is usually a mixture. The starting material is normally finely ground and is then called raw flour. The starting material may contain mineralizers, which are substances that lower the temperature necessary for melting and / or act as fluxes and / or improve clinker formation, for example, by forming solid solutions or by stabilizing the phases. Mineralizers can be part of the starting material components or added as a separate component.

Cement is used to designate a material that, after mixing with a liquid to form a paste, can develop mechanical strength by hydraulic reaction. Thus, cement indicates a ground clinker with or without more components and other mixtures such as supersulphated cement, geopolymer binder and dicalcium silicate cement obtained by hydrothermal treatment. Binder or binder mixture means a cement-containing material or mixture that develops mechanical strength by hydraulic reaction with water or otherwise such as carbonation, where the binder normally, but not necessarily, contains more components in addition to cement. A binder is used by adding water or other liquid and mostly also adding, as well as optionally mixtures and / or additives.

The binder from which the building element according to the invention is formed can be made from a wide variety of materials, including by-products and waste which, hitherto, cannot be used or can only be used to a limited extent. Regardless of the binder manufacture, which may or may not save energy compared to the production of other binders, there is a significant reduction in CO ² generation, since curing consumes CO ² .

Compared to known binders which harden by carbonation the binder according to the invention neither requires high grade raw materials nor does it require expensive and demanding curing. The manufacture of a clinker comprising ternesite, dicalcium silicate and ye'elimita allows the use of low grade raw materials and requires lower temperatures than for many other types of clinkers. Due to self-drying, CO ² can more easily access the entire structure in gaseous form, so that even at low temperature and with low CO ² concentration and pressure, rapid carbonation is achieved. Previous proposals were based on the dissolution of CO ² in water and temperatures of 90 ° C. Increasing temperatures for curing consumes part of the CO ² savings achieved and also requires elaborate devices. The binder paste according to the invention can be melted as Portland cement (OPC) and hardens under ambient conditions as OPC.

An important characteristic of the binder according to the invention is that both hydraulically reactive phases and phases that harden by carbonation are available. The proportion of hydraulic phases in the binder can be 28% to 100% by weight. Preferably at least 40% by weight is contained, more preferred at least 50% by weight and most preferred at least 60% by weight of hydraulic phases.

The most important hydraulically reactive phases are: ternesite, dicalcium silicate and ye'elimite. Furthermore, the ferritic phases C6AxFy with xy = 3 and both x and y> 0 and x <y, p, are suitable. ex. C ⁴ AF, C ² F, ellestadite and amorphous hydraulic phases of XRD, e.g. eg, glass-like materials, sludge and ash. Alita is possible, but in view of the high energy and associated CO ² emission associated with its production it is less preferred. Unlike OPC, the binder according to the invention neither requires nor significantly benefits from wing as a hydraulic phase. There may be carbonatable phases in small amounts from the start, for example, periclase, free lime or portlandite. Typically, hydrated products of hydraulically reactive phases such as calcium-silicate hydrates, calcium-aluminum-silicate hydrates, aluminum-silicate hydrates, portlandite, brucite, stratlingite, hydrotalcite-type phases, and ettringite / AFm make up the majority of the carbonatable phases that contribute to maximum strength.

The setting mechanism of the binder according to the invention is illustrated in Figure 1. Initially, the binder particles B are suspended in water W, left side. The hydraulic reaction consumes water and provides a layer of hydrated H phases around the binder particles comprising hydraulically reactive phases, see medium. The consumed water leaves the pores P behind (self-drying) and the hydration product provides a first setting and hardening of the paste. Hydraulic reaction setting and hardening often provide products with sufficient green strength for mold release. Final carbonation hardening provides binder particles B with a layer L of hydrated and carbonate phases, see right hand side of figure. Of course, this very schematic figure simply illustrates the principle, the reality is more complex, for example, the binder particles can be completely converted into hydrated and carbonated phases. Also, carbonation can begin immediately, although the main part of carbonation takes place only when the hydraulic reaction has created pores and hydrates. Hydrated phases may remain in the final product. Binder particles containing only carbonation phases will not hydrate.

In order to allow self-drying to take place the water / binder ratio (w / b) of the binder paste according to the invention has to be carefully adjusted. It may have a value of 0.2 to 1.2, preferably 0.25 to 0.8 and most preferably 0.35 to 0.6 with respect to the sum of the hydraulically reactive phases of the binder. Naturally, the w / b has to be tailored to the target properties of the product.

Additionally, the consistency of the dough has to be adapted. Since the w / b is normally low for binder pastes according to the invention it will often be necessary to add mixtures such as aqueous reducing agents, plasticizers and superplasticizers to adjust the consistency while maintaining the w / b in the proper range for self-drying. Useful aqueous reducing agents, plasticizers, and superplasticizers are, for example, but not exclusively, organic compounds with one or more of the following: carboxylate, sulfonate, phosphonate, phosphate, or alcohol functional groups. Other mixtures that influence workability are retardants. They are primarily intended to extend the time that a specified consistency is maintained. Retardants retard the setting and / or hardening of the binder paste. Suitable substances are, for example, but not exclusively, phosphates, borates, salts of Pb, Zn, Cu, As, Sb, lignosulfonates, hydroxylcarboxylic acid and its salts, phosphonates, sugars (saccharides).

Ternesite-dicalcium silicate-calcium sulfoaluminate (BCT) cements or ternesite-dicalcium silicate-calcium sulfoaluminate-ferrite (TBF) cements are used to provide the binder according to the invention. They can be done, for example, as described in WO 2013/023731 A2 (BCT) and WO 2013/023729 A2 (TBF), respectively. BCT and TBF cements contain high amounts of dicalcium silicate in addition to ternesite and ye'elimite and are often high in unwanted elements such as heavy metals. Their hydraulic properties are often not sufficient for use as a hydraulically hardening binder, but are too reactive for use as supplemental cementitious materials in OPC-based binders.

Typical compositions for BCT are:

8% to 75% by weight ternesite, preferably 10% to 60% by weight, most preferred 20% to 40% by weight;

15% to 70% by weight of dicalcium silicate, preferably 20% to 60% by weight, most preferably 30% to 50% by weight;

5% to 70% by weight of ye'elimits, preferably 10% to 60% by weight, most preferably 20% to 45% by weight;

0% to 30% by weight of C ⁴ AF, preferably 3% to 25% by weight, most preferably 5% to 15% by weight;

0% to 20% by weight of C ² F, preferably 2% to 15% by weight, most preferably 3% to 8% by weight;

0% to 30% by weight of hydraulic X-ray amorphous phase, preferably 2% to 25% by weight, most preferably 5% to 20% by weight;

0% to 30% by weight of minor phases.

Typical compositions for TBF are:

20% to 95% by weight ternesite, preferably 30% to 85% by weight, most preferred 40% to 75% by weight;

5% to 80% by weight of dicalcium silicate, preferably 15% to 70% by weight, most preferably 20% to 60% by weight;

5% to <15% by weight ye'elimits, preferably 5% to 12% by weight, most preferably 5% to 10% by weight;

0% to 30% by weight of C ⁴ AF, preferably 3% to 25% by weight, most preferably 5% to 20% by weight;

0% to 20% by weight of C ² F, preferably 2% to 15% by weight, most preferably 3% to 8% by weight;

0% to 30% by weight of hydraulic X-ray amorphous phase, preferably 2% to 25% by weight, most preferably 5% to 20% by weight;

0% to 30% by weight of minor phases.

All amounts relative to the total binder phases and provided that the sum of all the phases including the optional additional components add up to 100%. Minority amounts summarize components, hydraulic or not, that are contained in individual amounts less than 10% by weight, usually less than 5% by weight or even only in trace amounts. The usual minority phases are anhydrite, lime, periclase, quartz, hematite, Ca-langbeinite, maghemite, akermanite. In addition to these, there may be one or more of the following: y-belite, ellestadite, krotite, mayenite, grossite, srebrodolskite, hydroxyllestadite, gehlenite, abelite, rankinite, alite, calcite, dolomite, corundum, (para) wollastonite, forsterite, enstatite, fayalite, aluminate, magnetite , mullite, fluoro-chloro-apatite, dodecacalcium potassium fluoride-dioxide-tetrakis (silicate), arcanite, langbeinite, aphthitalite, thernadite, bassanite, gypsum, sylvite, halite, syngenite, portlandite, hydrated tetracalcium aluminate, hydrocalumite, monosulfate hydrate , perovskite, rutile, anatase, fluBspat, austenite, merwinite, bredigite, jasmundite and oldhamite.

These cements can be made using large quantities of industrial by-products and low-grade precursor materials not applicable for the production of OPC in substantial quantities such as sludge, ash, quarry overburden, quarry dust, demolished construction waste, glass residue, waste from plaster and mixtures thereof.

The raw materials are selected and if necessary mixed to provide a suitable raw flour. An adapted Bogue calculation can be used to determine suitable amounts. The raw flour is converted, for example, in a rotary kiln fitted with a device to temper the clinker to ensure a sufficient content of ternesite. The clinker is then ground to obtain the cement. Normally, other components such as mixtures and especially additives are mixed with the cement to make the binder, but the cement can also be used without additives. The clinker as well as the cement and the binder obtained will normally have a low content of calcium compared to an OPC, rendering many such cements useless for only conventional hydraulic hardening. But according to the invention the low hydraulic reactivity provided is sufficient since rapid carbonation provides the necessary resistance, often very high resistance, at suitable times.

The BCT and TBF clinkers may have a composition that allows their use as a binder according to the invention on their own. In many cases, especially TBF clinkers will combine e.g. ex. with clinker or calcium sulfoaluminate cement to increase the content of ye'elimite and / or OPC or another clinker or belite cement to increase the dicalcium silicate. Also, the addition of sulfate is contemplated if its amount is as low as desirable. A useful composition for the binder is:

• 8% to 75% by weight ternesite, preferably 10% to 60% by weight, most preferably 20% to 40% by weight;

• 15% to 80% by weight of dicalcium silicate, preferably 10% to 60% by weight, most preferably 20% to 50% by weight;

• from 5% to 70% by weight of ye'elimita, preferably from 10% to 60% by weight, most preferred from 20% to 45% by weight;

• 0 to 50% by weight of C6AxFy with x y = 3 and both x and y> 0 and x <y, preferably 3% to 25% by weight, most preferably 5% to 15% by weight;

• 0% to 20% by weight of reactive aluminates, preferably 0.5% to 10% by weight, most preferred 1% to 5% by weight;

• 0% to 25% by weight of periclase, preferably 1% to 20% by weight, most preferably 3% to 10% by weight;

• 0% to 30% by weight of hydraulic X-ray amorphous phase, preferably 2% to 25% by weight, most preferred 5% to 20% by weight and

• 0% to 30% by weight of minor phases, preferably 0% to 15% by weight, most preferably 0% to 5% by weight.

The binder used to make the building blocks according to the invention may contain customary mixtures and / or additives. Known mixtures and / or additives for OPC are useful, as well as specific ones adapted to other binders such as calcium sulfoaluminate cement and calcium aluminate cement.

Frequently used mixtures are aqueous reducing agents and plasticizers such as, but not exclusively, organic compounds with one or more of the following: carboxylate, sulfonate, phosphonate, phosphate, or alcohol functional groups. These serve to achieve a good consistency, ie flowability, of the paste with a smaller amount of water. Since a decrease in w / b normally provides an increase in strength, such mixes are commonly used. Air-entraining agents can also improve flowability and can be used for this purpose or for other reasons such as, but not limited to, density modifications and compactability improvements.

Furthermore, it is possible to add activators that increase the hydraulic reactivity of the cement phases and / or the carbonation activity of the hydrates and the anhydrous phases. Examples of such substances are, for example, hydroxides, nitrates, sulfates, chlorides, silicates (hydro) carbonates of alkali and alkaline earth metals or organic compounds such as glycerin, organic acids and their salts, cyanates and amines, for example, triethanolamine, triisopropanolamine, diethanoisopropanolamine. It should be noted that some of these can act as retarders and accelerators depending on the dose.

Special mixtures can be added to improve the dissolution of the carbonate ions in the interaction solutions and consequently speed up the carbonation process. These can be aqueous solvents such as alkanolamines, for example, primary amines type monoethanolamine (MEA) and diglycolamine (DGA), secondary amines type diethanolamine (DEA) and diisopropanolamine (DIPA) and tertiary amines type methyldiethanolamine (MDEA) and triethanolamine (TEA) or any mixture of them or soluble alkali salts and hydroxides or other substances that can be used to improve the dissolution of CO ² in the solution. Additionally, enzymes such as carbonic anhydrase (CA) can be used to improve the efficiency of carbonation and modify the properties of the reaction products. It should be noted that these mixtures not only have one action but can also perform a double function. They can modify the hydration process as well as modify the carbonation process as well as the morphology and microstructure of the products formed. The effect can be highly dose dependent.

It is also possible to add mixtures that modify the morphology of the calcite that precipitates during the hydration and carbonation process. This provides the advantage of forming less dense shales of hydrate and carbonate products and allows higher degrees of carbonation and hydration. Suitable are, for example, magnesium salts, polyacrylic acids, polyacrylamide, polyvinyl alcohol, polyvinylsulfonic acids, styrene sulfonate, citric acid and other organic acids, polysaccharides and other substances, e.g. eg, phosphonates, polycarboxylates. It should be noted that these mixtures not only have one action but can also perform a double function.

In addition, it is possible to add mixtures that regulate the pH during the hydration and carbonation process to improve the precipitation of calcite, these include metal hydroxides and carbonates and similar substances. It should be noted that these mixtures do not have a single action but can have a double function.

All mixtures are used in the amounts known as such, where the amount is tailored to a specific binder and special needs in known manner.

Additives are, for example, fillers, pigments, reinforcing elements, self-curing agents. Typical fillers are mineral particles such as stone dust as well as fibers such as glass, metal and / or polymer fibers. An addition that is also used as a supplemental cementitious material is silica fume. All of these can be added in amounts known per se.

A preferred use of the binder according to the invention is precast concrete and production of concrete articles. The binder is normally mixed with aggregate and water as well as with mixtures and / or additives as desired. The building material thus obtained is then used as it is known per se.

Unlike known hydraulically hardening materials carbonation follows when the hydraulic reaction provides sufficient porosity. Thus, hardening should not take place in water or with constant water supply. Instead an atmosphere is provided which contains CO ² and which is preferably rich in CO ² . Unlike the materials that harden by carbonation, the binder according to the invention and the construction materials that contain it need water in a defined quantity to provide the first set (and hardening if applicable) including the creation of additional porosity.

Carbonation to final hardening requires CO ² which is present in the normal atmosphere. To achieve hardening in acceptable times, carbonation is accelerated by supplying an atmosphere rich in CO ² . For example, the molds can be placed inside a suitable space and exhaust gas rich in CO ² , e.g., is passed into the space. eg, flue gas from cement kilns.

Curing time depends on process conditions and material composition such as temperature, CO ² pressure, water vapor pressure, sample thickness, water to cement ratio, number of hydraulically reactive phases. , hydrates formed prior to carbonation, porosity of concrete. Typical carbonation times for CO ² pressure in the range 0.005 MPa to 2 MPa, preferably 0.05 MPa to 0.5 MPa and temperatures from room to 100 ° C, preferably up to 50 ° C, most preferred to room meaning from 15 ° C to 35 ° C, it is from 10 minutes to 48 hours.

The building element obtained after final hardening by carbonation normally exhibits high strength and durability.

The invention will be further illustrated with reference to the examples that follow, without restricting the scope to the specific embodiments described. If not otherwise specified any amount in percentage or parts is by weight and in case of doubt with reference to the total weight of the relevant composition / mixture.

The invention further includes all compositions with characteristics described and especially with preferred characteristics that are not mutually exclusive. A characterization such as "about", "about" and expressions Similar in relation to a numerical value means that values up to 10% higher and lower are included, preferably values up to 5% higher and lower and in any case values at least up to 1% higher and lower, the exact value being the value or the most preferred limit.

The term "substantially free" means that a particular material is not purposely added to a composition and is only present in trace amounts or as an impurity. As used herein, unless otherwise indicated, the term "free of" means that a composition does not comprise a particular material, ie, the composition comprises zero percent by weight of said material.

Example 1

A TBF cement with an oxide composition presented in table 1 was used. It contained, according to Rietveld's XRD, 23.6% by weight of ternesite, 23.3% by weight of dicalcium silicate, 11.8% by weight of ye'elimite, 6.1% in weight of C ⁴ AF, 3.7% by weight of C ² F, 19.2% by weight of amorphous hydraulic phase and 12.3% by weight of minor phases, including anhydrite, lime, periclase, quartz, hematite, Ca-langbeinite, maghemite, akermanite , each in an amount below 2% by weight. The density was 3.16 g / cm3, the fineness according to Blaine 2020 cm2 / g.

Table 1

If they made samples of water, cement and sand mortar in a weight ratio of 0.5: 1: 1.3 and water and cement pastes in a 0.5: 1 ratio. Mixing was carried out in a Hobart mixer, 15 s slow and 15 s fast as specified in EN 196. All samples were initially hydrated for 18 h in sealed containers at 50 ° C. The samples were then dried in an oven at 50 ° C and stored in ambient air at 20 ° C and relative humidity of approximately 55% (reference sample) or below 250 Pa (2.5 bar) of CO ² at 20 ° C (carbonated sample). The pasta samples were ground to <2 mm before storage in ambient air or under CO ² pressure. The compressive strength of the hardened mortar samples was determined according to the procedure specified in EN 196 and hardened pastes and mortars were examined with thermogravimetry on a Netzsch Jupiter STA 449 device.

The compressive strength of the samples is represented in fig. 2, it can be seen that carbonation almost doubles the compressive strength. The samples gained an average of 0.6 g, corresponding to a cement mass of approximately 10% during carbonation. This mass change includes ^{bound CO 2} as well as water lost during carbonation. To distinguish between these two mass changes, a differential thermogravimetric (TG) analysis was done.

The results of TG measurements of the hardened paste and mortar are shown in Figure 3. The weight loss from about 500 ° C to about 850 ° C shows that a significant amount of calcite was formed during carbonation. The pastes gained approximately 28% of calcite which corresponds to a mass gain of approximately 15% and the mortars gained approximately 13% of calcite which corresponds to approximately 6% of mortar mass which corresponds to approximately 14% of cement mass.

Example 2

The same clinker was used as in Example 1, however it was ground to a fineness of 2910 cm2 / g according to Blaine. Mortar and paste samples were made in a manner analogous to Example 1. All samples were initially hydrated for 24 h in sealed containers at 50 ° C. The samples were then treated with one or more of the following:

D: drying 24 h in an oven at 50 ° C,

L: stored 24 h in ambient air at 20 ° C and relative humidity of approximately 55% CO2: stored 24 h with 250 Pa (2.5 bar) of CO ² at 20 ° C.

The compressive strength and density of the hardened mortar samples were determined according to the procedure described in EN 196 and the hardened pastes and mortars were examined thermogravimetrically on a Netzsch Jupiter STA 449 device.

Figure 4 shows the compressive strength and density measured in mortar samples. Comparison of strength for sample C-CO2 that is hydrated and carbonated with CL that only hydrates (but hydrates for longer than C-CO2) shows that carbonation improves hardening, greater strength is gained by subsequent carbonation than with prolonged hydration. High temperature drying increases the hardening itself by accelerating hydration and enhancing carbonation. Thus, the CD sample that only hydrates but for a longer time than the CL sample presents greater resistance, but carrying out carbonation according to the invention provides a much greater resistance as the CD-CO2 sample exhibits. These findings are confirmed by the measured densities. The 0.1 g / cm3 gained corresponds to the CO ² bound in the carbonated samples.

The result of different thermogravimetric analysis is shown in Figures 5a and 5b. It can be seen in figure 5a that drying does not change the hydrates formed initially, compared to sample C only hydrated with sample CD which was hydrated and dried in an oven. During carbonation with 250 Pa (2.5 bar) of CO ^2, the hydrates partially decompose and form carbonates, comparing the C + CO2 and C + D + CO2 samples with the C sample in fig. 5b. The mass loss between ~ 500 ° C and ~ 850 ° C is due to the decomposition of CaCO3 and shows that approximately 40% of CaO is bound as carbonate during carbonation.

The XRD spectra are shown in Figure 6. The TG result is confirmed, that is, drying does not change the hydrates. Furthermore, AFm carbonation takes place in all samples carbonated with 250 Pa (2.5 bar) of CO ² . Ettringite carbonation only takes place in dry samples.

Example 3

Mortars and pastes were made in a manner analogous to that of Example 2 from the cement used in Example 1. In addition to the treatments in Example 2, the samples were carbonated by placing them 24 h in the chimney of the operating cement plant. Thus, carbonation took place in exhaust gas from cement plants for so-called PI samples. As in Example 2, resistance and thermogravimetric behavior were measured. The results are shown in figure 7a and 7b and confirm that the exhaust gas from cement plants is a very suitable medium for carbonation.

Finally, the depth of carbonation was measured by spraying 1% by weight thymophthalein in a mixture of 70% by volume ethanol and 30% by volume water. None of the exhaust gas carbonated samples showed coloration, that is, they were fully carbonated. In contrast, reference samples that were only dried or stored in ambient air were intensely colored.

Claims (15)

1. Method to manufacture building elements that includes the steps: - provide a binder comprising at least 8% by weight of ternesite, at least 15% by weight of dicalcium silicate and at least 5% by weight of ye'elimita, each with respect to the total binder, as hydraulically phases reactive - mix the binder with water to form a paste - melt the paste into the desired shape for the construction element - hydraulically reacting the paste to form hydrated phases and create additional capillary pores and - harden by carbonation to provide the building element. Method according to claim 1, wherein the binder contains at least 28% by weight, preferably at least 40% by weight, more preferred at least 50% by weight and most preferably at least 60% by weight hydraulically reactive phases relative to total binder weight. 3. Method according to claim 1 or 2, wherein in addition to ternesite, dicalcium silicate and ye'elimita, at least one of the hydraulically reactive phases is contained: ellestadite, ferritic phases and amorphous hydraulic phases. 4. Method according to any of claims 1 to 3, wherein the ratio of water to binder with respect to the sum of hydraulically reactive phases in the binder is set from 0.2 to 1.2, preferably from 0.25 to 0.8 and most preferably from 0.35 to 0.6. 5. Method according to any one of claims 1 to 4, wherein the hydrated products of the hydraulically reactive phases comprising calcium-silicate hydrates, calcium-aluminum-silicate hydrates, aluminum-silicate hydrates, portlandite, brucite, stratlingite Hydrotalcite and ettringite / AFm type phases form most of the carbonation hardening phases. 6. Method according to any one of claims 1 to 5, wherein there is in the binder periclase and / or free lime that harden by carbonation from the beginning in an amount of up to 15% by weight of each and up to 30% combined. 7. Method according to any one of claims 1 to 6, wherein aqueous reducing agents, plasticizers and / or superplasticizers are added to adjust the consistency while maintaining the w / b in the proper range for self-drying. 8. Method according to any one of claims 1 to 7, wherein air-entraining agents are added to the binder. Method according to any one of claims 1 to 8, wherein additives, preferably fillers, pigments, reinforcing elements, self-healing agents or a mixture of two or more of them are added. 10. Method according to any one of claims 1 to 9, wherein the binder contains: 15% to 80% by weight of dicalcium silicate, from 5% to 70% by weight of ye'elimita, 0% to 50% by weight of C6AxFy with x y = 3 and both x and y> 0 and x <y, 0% to 20% by weight of reactive aluminates 0% to 30% by weight of amorphous phase by hydraulic X-ray, 0% to 30% by weight of minority phases, all with respect to the total amount of binder. Method according to any one of claims 1 to 10, wherein the paste is subjected to hydraulic hardening in an atmosphere of 40% to 99% relative humidity and at a temperature of 10 ° C to 80 ° C. Method according to claim 1 to 11, wherein carbonation takes place in a CO ² rich atmosphere preferably having a CO ² pressure of 0.005 MPa to 2 MPa, preferably 0.05 MPa to 0.5 MPa and a temperature in the range from 15 to 35 ° C up to 100 ° C, preferably up to 50 ° C. A method according to claim 12, wherein CO ^2- rich exhaust gas, preferably cement kiln flue gas, is used to provide the CO ^2- rich atmosphere. 14. Building elements obtainable from a binder comprising at least 8% by weight of ternesite, at least 15% by weight of dicalcium silicate and at least 5% by weight of ye'elimits as hydraulically reactive phases by a method according to any one of claims 1 to 13. Building element according to claim 14 in the form of a precast concrete element.